With the development of information technology, touch panels have gradually replaced conventional mouses and keyboards and are widely used in various electric products, due to its humanization design and convenience in operation for input. Among the touch panels, capacitive touch panel has been widely applied due to its fast response speed, high touch sensitivity, good reliability and high endurance. The capacitive touch panel mainly includes a cover lens and a touch sensor, whose working principle is described as below. A voltage is applied to four corners of the touch panel to form a fixed electric field. When a finger touches the screen, a capacitance between the human body and a transparent electrode of the touch sensor is changed, and an electric current is accordingly generated under the electric field. The touched position can be calculated out by a controller according to the different distances from the position where the electric current is generated to the four corners of the touch panel.
Based on different arrangements of the touch sensor in a display panel, the touch display panel includes the following types: add-on type, one glass solution (OGS), In-Cell type, and On-Cell type. In an add-on type touch display panel, the touch sensor and the display panel are separated formed and then assembled together to cause the product to be relatively thicker, failing to meet the ultra-thin requirement of some handheld portable electronic devices. In an OGS touch display panel, the touch sensor and the cover lens are integrated together and then adhered to the display panel by an optically clear adhesive, having the advantage of high touch sensitivity and the disadvantage of poor strength and being fragile. In an In-Cell type touch display panel, the touch sensor is formed on an inner surface of a color filter (CF) substrate of the display panel, having a low production yield due to its complicated structure and manufacturing process. In an On-Cell touch display panel, the touch sensor is formed on an outer surface of the color filter substrate of the display panel, the touch sensor being embedded between the color filter substrate and the top polarizer.
FIG. 1 is a cross-sectional view of a conventional touch display panel, FIG. 2 is a schematic view of an electric field distribution of the touch sensor in FIG. 1, and FIG. 3 is a planar schematic view of the touch sensor in the conventional touch display panel. Referring to FIGS. 1 to 3, a conventional touch display panel 20 includes, from the bottom to the top, a thin-film transistor (TFT) substrate 21, a liquid crystal (LC) layer 22, a color filter (CF) substrate 23, a touch sensor 24, a top polarizer (POL) 25 and a cover lens 26, wherein an emission electrode (Tx) 241 and a receiving electrode (Rx) 242 of the touch sensor 24 are arranged at different layers, therefore a vertical electric field is formed between the emission electrode 241 and the receiving electrode 242 (FIG. 2). The emission electrode 241 and the receiving electrode 242 are spaced from each other and in the form of metal mesh, an extension direction of the emission electrode 241 is orthogonal to an extension direction of the receiving electrode 242.
The metal mesh of the electrodes 241, 242 have small resistance and high light transmission. However, since the emission electrode 241 and the receiving electrode 242 are arranged at different layers, when light transmits through the emission electrode 241 and the receiving electrode 242, an interference phenomenon will occur separately in each of the different layers. Thus, a serious Moire fringe will be introduced, and the display effect of the display panel is impacted. Meanwhile, on the touch sensor 24, there is an exposed area 243 which is not covered by either the emission electrode 241 or the receiving electrode 242. The exposed area 243 causes the pattern of the touch sensor 24 to be uneven, resulting in difference in light transmission and affecting the display quality of the touch display panel.